DE102009026590A1 - Detecting the leaving of an operating range of a fuel cell system and initiating the necessary steps - Google Patents

Abstract

The invention relates to a method for operating a fuel cell system (1) with at least one fuel cell (2), wherein a mass flow (10) flows through the fuel cell (2). According to the invention, the method includes a first step for detecting a deviation from an allowable operating range (B), wherein the first step comprises the following individual steps: Defining the permissible operating range (B) by permitting a mass flow value $ I1 permissible pressure differences (ΔP ) from a first pressure (P) of the mass flow (10) before the fuel cell (2) and a second pressure (P) of the mass flow (10) to the fuel cell (2) within tolerance limits (B ', B' ') are assigned Measuring the first pressure (P) before entry of the mass flow (10) into the fuel cell (2) at a time · measuring the second pressure (P) after an exit of the mass flow (10) from the fuel cell (2) at the time · Closing to a deviation from the permissible operating range (B) when an operating point (A, A, A, A, A, A) flowing through an allocation of the mass flow value $ I2 of, in particular at the same time mass flow (10) to a measured pressure difference (ΔP) from the measured first pressure (P) and the measured second pressure (P) is characterized, outside the tolerance limits (B ', B' ') of the permissible operating range (B) is and that the procedure a ...

Description

The The invention relates to a method for operating a fuel cell system with at least one fuel cell according to The preamble of claim 1, wherein a mass flow is the fuel cell flows through. Furthermore, the invention relates to a fuel cell system according to the preamble of claim 13.

State of the art

A Fuel cell is powered by different mass flows, such as a cathode current, an anode current and / or a coolant flow. To ensure proper operation of the fuel cell To ensure it is necessary that the mass flows flow through the fuel cell in the desired strength. Therefore, the channels in which the mass flows flow, have no leakage or such a leak should be detected: As a channel in the following any kind of pipeline, hose, flowfield or the like, through which a mass flow can flow. For example Leakage in a cathode current can lead to undersupply the fuel cell with oxygen and thus damage lead a membrane of the fuel cell.

The publication DE 10 2006 008 254 A1 discloses a fuel cell assembly in which a leakage between a space in which a fuel gas is located and a space in which oxygen-containing air is located by measuring the oxygen content of the air at the exit from the fuel cell can be closed. Preferably, by measuring the oxygen content of the air in front of the fuel cell, by measuring the oxygen content of the air after the fuel cell and by measuring the volume flow of the air to a leak. The disadvantage here is that only a leak and only a leak between the above-mentioned spaces in the presence of oxygen can be detected. In addition, the gas pressure on the side of the fuel gas must be necessarily higher than the gas pressure of the air. Another disadvantage is that this costly lambda probes, paramagnetic detectors, mass spectrometers or gas chromatographs must be used.

One Another obstacle to proper operation of a fuel cell system are fixed and / or in the case of a gaseous mass flow, also liquid accumulations in the channels showing a pressure drop of the mass flow increase. Here, in particular, a cold start of a fuel cell system, z. B. when installing the fuel cell system in a vehicle, can freeze in the water in the channel, so worst If the channel even freezes, call. Also in this case can for the example of a freezing channel of a cathode current to damage the membrane of the fuel cell Undersupply of oxygen.

Disclosure of the invention

It It is an object of the invention to provide a method which is a disorder through improper channels that z. As a leak or solid or liquid accumulations exhibit, recognize and correct or avoid in advance. in this connection the process should be simple and inexpensive. The Procedure should be independent of the type of mass flow be. Also, the method should not focus on a type of disorder, z. As leakage, be limited, but several types of Detect and / or avoid faults. It is also an object of the invention to provide a fuel cell system with which such a procedure is applicable.

to Solution of the task becomes a procedure with the characteristics of claim 1, in particular of the characterizing part proposed. Advantageous developments of the method are in the dependent Specified method claims. The task will continue solved by a fuel cell system of the independent Claim 13, in particular of the characterizing part.

advantageous Further developments of the fuel cell system are in the dependent Device claims specified. Features and details, in connection with the method according to the invention are described, of course, apply as well in connection with the fuel cell system according to the invention and vice versa. It can in the claims and in the description mentioned features individually be inventive in itself or in combination.

In the method according to the invention, two basic steps are provided. In a first step (step I.) it is detected whether a deviation from a permissible operating range which has been previously determined. The permissible operating range is to be understood as an operating range in which the fuel cell system usually operates without interference and in particular without damaging the fuel cell. In a second step (step II.) Can be concluded on the basis of the nature of deviation, ie whether and in which direction and / or how much and / or under what conditions from the operating range, a specific disorder and the necessary measures to overcome / slowdown this disorder are taken. Alternatively, the permissible operating range can be intentionally abandoned, for example, to prevent a fault. Here, the method according to the invention serves to monitor the departure from the permissible operating range. In the second step, drawing a conclusion as to what type of disturbance it is or whether the allowable operating range has been properly exited may be understood as the generation of a triggering event, the generation followed by a sequence signal.

Under Deviating from the permissible operating range, an over- or below the permissible operating range become. The fuel cell system can be previously in the permissible operating range and when deviating the leave the permitted operating range. But it can too z. B. be at a cold start that the fuel cell system previously not in the permitted operating range so that a departure is generally considered to be outside the permissible operating range are independent understood from an initial state of the fuel cell system can be.

Around in the first step of the method, deviating from the permissible one Recognize operating range, the procedure provides that the permissible Operating range is initially set (single step I.A.). Here, a mass flow value permissible pressure differences from a first pressure of the mass flow in front of the fuel cell and a second pressure of the mass flow after the fuel cell assigned. The assignment takes place for at least one mass flow value instead of. However, different possible mass flow values are preferred each admissible pressure differences assigned. The pressure differences lie within tolerance limits, which are for the trouble-free and no causing damage Operating the fuel cell system are characteristic. in this connection The allowed operating range can be different Operating conditions such as temperature, power production and humidity, include allowable pressure differences to a mass flow value.

While the operation becomes the first pressure before entry of the mass flow measured in the fuel cell with a first pressure sensor (single step I. B.). At the same time, the second pressure after an exit of the Mass flow from the fuel cell with a second pressure sensor measured (single step I. C.). Thereafter, in single step I. D. the pressure difference of the first and the second pressure formed. A mass flow value can be the measured pressure difference from the first measured and the second measured pressure are assigned, so that an operating point of the fuel cell system by the assignment of these Pressure difference is defined to the mass flow value. In which the Measured pressure difference associated mass flow value is is the indication of the strength of the mass flow at the moment flows in the fuel cell system. In particular, the Mass flow value of the mass flow, which coincides with the measurements of the first and second pressure flows. After that can be checked whether the operating point thus obtained within the tolerance limits of the permissible operating range lies. If the operating point is outside the permissible limit Operating range, there is a deviation from the permissible Operating area. In order for a deviation from the permissible It can also be sufficient to close the operating range be if from at least one operating parameter of the fuel cell system a position of the operating point outside the tolerance limits can be closed without explicitly determining the operating point.

Especially it is possible that single step I. B. to I. D. several times, especially continuously during operation be performed of the fuel cell system. there The operating range may or may not be reset each time but the determination of the permissible operating range (Single step I.A.) may be prior to operation of the fuel cell system once or during operation once, continuously, at intervals or depending on other conditions be determined. Will a deviation from the permissible Operating range in single step I. D. found, it works Procedure to step II.

Thereby, that a characteristic characteristic of all mass flows, namely the pressure used in the present process is that Method on all a fuel cell flowing mass flows applicable, such as a cathode current, an anode current or a coolant flow. The process is very different Interference applicable, which is a change in the pressure difference cause. These include density changes in the Mass flow, cross-sectional changes or changes in length in a channel through which the mass flow passes or changes the channel texture or texture of the built-in canal Elements. In particular, the method can both for the detection of a Leakage as well as to detect the presence of a fixed or liquid substance and thus in particular for detection a blockage can be used within the channel. Since that Process only two pressure sensors and possibly a mass flow sensor needed, it is very cost effective.

To set the permissible operating range, it may be provided that the determination takes place before the actual operation of the fuel cell system. For this purpose, different pressure differences can be specified and, for this purpose, possible mass flow values are measured, which are characteristic for almost optimum operation, so that a measurement curve is produced. Conversely, the mass flow value can also be predetermined and permissible pressure differences can be measured. A tolerance range may, for example, result from the fact that different humidity or temperature fluctuations of the mass flow are possible without affecting the operation of the fuel cell. In order to keep the tolerance range as small as possible, it may be useful to define several operating ranges depending on an additional parameter such as current or power of the fuel cell or moisture of the mass flow. During operation, the additional measured variable is then likewise determined and the corresponding permissible operating range is used in the method according to the invention. By determining the permissible operating range, which remains unchanged during operation of the fuel cell system, even creeping disturbances can be detected. Before the operation of the fuel cell system, additional ranges of pressure difference and mass flow value can be determined by measurement series that do not correspond to an optimal operating state, but whose knowledge is still helpful, for example, an area that corresponds to a particularly dry channel.

Alternatively, the allowable operating range can be set during operation. If a quadratic dependence of the mass flow value ṁ on the pressure difference ΔP according to a throttle model according to the following equation (1) is assumed, the parameters a ₀ , a ₁ and a ₂ can be determined after running through several states in a trouble-free operation, so that the permissible operating range. Alternatively, the parameters a ₀ , a ₁ and a _{2 are} initially taken from a series of measurements before operation. ΔP = a 0 + a 1 · Ṁ + a 2 · (M ') 2 Equation (1)

If the measured mass flow value deviates from the mass flow value calculated using the given parameters according to equation (1), then the parameters a ₀ , a ₁ and a _{2 can be} adapted or a tolerance range can be defined for the parameters a ₀ , a ₁ and a ₂ . An advantage of this type of determination is that little or no previous knowledge is necessary and that the permissible operating range can adapt to varying operating conditions. The disadvantage is that, in particular with gradual changes can not be concluded without additional information between a change in the permissible operating range due to changed operating conditions or a fault.

It may be that the mass flow value, in single step I. D. the measured pressure difference is assigned, a measured mass flow value is, in particular, at the same time as the first and the second Pressure measured with a mass flow sensor, d. H. the inventive Method has a further single step in addition to the individual steps I. B. and I. C., in which a further Size, the mass flow value, measured and not is closed from other measured values. Usually will be the measurement of the mass flow value at the same intervals or preferably continuously as the measurement of the first and second Pressure made. To find out if the operating point is outside the permissible operating range is the permissible pressure differences to the measured mass flow value be compared with the measured pressure difference. Yields the Comparison that the pressure differences do not correspond within tolerance limits, so it is concluded that there is a deviation from the operating range. alternative can at a predetermined, adjusted pressure difference of the measured Mass flow value with the permissible mass flow value of predetermined pressure difference can be compared.

In the alternative case, it may be that the fuel cell system has no mass flow sensor, but the mass flow value, which is assigned in a single step ID of the measured pressure difference, adjusted and characterized by means of controller signals. A loop structure is a mass flow value, as z. B. is necessary to generate a required power of the fuel cell, and given a first target pressure. This mass flow value, which is referred to below as the "predetermined mass flow value", is first assigned an admissible pressure difference in the control loop structure and a second setpoint pressure is determined on the basis of this permissible pressure difference and the first set pressure. The first and second set pressures are transmitted to the controller. The measured pressures are also transmitted to the controller. The controller now outputs control signals to set a mass flow value in which the measured pressures and the set pressures are in agreement. Since the mass flow value to be set can already be deduced by the controller signals, it is possible to detect a deviation from the permissible operating range on the basis of the controller signals, without the mass flow value to be set to be determined explicitly. This means that in individual step ID, even without explicit knowledge of the operating point, it is possible to conclude that there is a deviation from the permissible operating range, since the controller signals indicate that the operating point is outside the permissible operating state indicate area.

Especially it is conceivable that the mass flow value before the fuel cell and measured upstream of the first pressure sensor in the flow direction and all the conclusions below Unless otherwise mentioned, this. Generally is However, it is also possible that the mass flow value behind the second pressure sensor and between the first and the second Pressure sensor is measured. In this case may need other conclusions from exceeding or falling short of the tolerance limits are drawn.

Examples for the second step of the method will be exemplified discussed in the embodiments.

The Invention is also solved by a fuel cell system, operated with the inventive method can be. For this purpose, the fuel cell system has a first Pressure sensor for measuring the first pressure and a second pressure sensor to measure the second pressure. Furthermore, the system must have a monitoring unit with which it can be determined whether the fuel cell system is within the permissible operating range. The monitoring unit will, when the permissible operating range is exceeded is to initiate appropriate measures of derogation. If the mass flow value is measured, then there is still a Mass flow sensor in the fuel cell system. Preferred is first the mass flow sensor, then the first pressure sensor, then the fuel cell and then the second pressure sensor, in the flow direction considered, arranged.

Instead of A fuel cell may also use a fuel cell stack become.

Further the invention improving measures will be apparent from the following description of embodiments of the Invention, which are shown schematically in the figures. All from the claims, the description or the drawing Outstanding features and / or benefits, including constructive details, spatial arrangement and method steps can both for yourself and in various combinations be essential to the invention. Show it

1 Section of a fuel cell system according to the invention

2 Pressure difference over mass flow value plot with allowable operating range and operating points in case of leakage

3 Pressure difference over mass flow value plot with allowable operating range, dry channel operating range and wet and / or freezing channel operating range

4 Control loop structure according to the invention

In 1 is a schematic part 1' a fuel cell system 1 with a fuel cell stack 2 shown. This is the path of a cathode current 10 who owns the fuel cell system 1 as indicated by the arrows 11 marked flow direction in a channel 5 passes. As cathode current 10 For example, ambient air from a compressor 3 sucked and compressed. The compressed cathode current 10 gets in a humidifier 4 moistened and goes through a humidifier chamber 4 ' , The so moistened cathode current 10 reaches the fuel cell stack 2 with a first pressure P ₁ . In the fuel cell stack 2 At least a portion of this reacts in the cathode stream 10 contained oxygen from the ambient air in an electrochemical reaction to water, thereby generating electricity. The cathode current 10 leaves the fuel cell stack 2 with a second pressure P ₂ . The second pressure P ₂ is opposite to the first pressure P ₁ due to the pressure loss due to pipe friction within the duct 5 that is inside the fuel cell stack 2 lies, and reduces flow resistance etc. Among other things, the pressure loss depends on the density of the cathode current and the diameter of the channel 5 inside the fuel cell stack 2 from. Furthermore, gases from anode chambers of the fuel cell stack 2 in the cathode current 10 be diffused. The second pressure P ₂ is also changed with respect to the first pressure P ₁ , since the cathode current 10 at the exit from the fuel cell stack 2 released oxygen and absorbed water through the electrochemical reaction. The first pressure P ₁ and the second pressure P ₂ are also temperature-dependent. After leaving the fuel cell stack 2 the cathode current passes through 10 another humidifier chamber 4 '' to add moisture to the incoming cathode stream 10 leave. By a back pressure control valve 6 the second pressure P _{2 can be} regulated. Thereafter, the cathode current leaves 10 the fuel cell system 1 and is returned to the environment.

According to the invention, the first pressure P ₁ with a first pressure sensor 8th in front of the fuel cell stack 2 and the second pressure P ₂ with a second pressure sensor 9 after the fuel cell stack 2 measured. If no mass flow value ṁ is measured, then the first pressure P ₁ and the second pressure P _{2 are} adjusted. For this purpose, a monitoring unit 14 be provided by transmission lines 15 . 16 the values for the first pressure P ₁ and receives the second pressure P ₂ and the one speed n of the compressor 3 and a position of the backpressure control valve 6 , which is predetermined by a control voltage U, according to the arrows 12 . 13 pretends. This results in a loop structure 18 according to 4 , Alternatively, the strength of the cathode current 10 , ie the mass flow value ṁ, of a mass flow sensor 7 in particular in front of the compressor 3 can be arranged to be measured. In this case, the mass flow value ṁ can be adjusted by the mass flow value ṁ over the transmission path 17 to the monitoring unit 14 is transmitted and the monitoring unit 14 over the transmission line 12 the speed n of the compressor 3 and over the transmission line 13 specifies the control voltage U of the back pressure control valve. The measured pressures P ₁ and P ₂ are used in this case to monitor a deviation from an allowable operating range B. But even if the mass flow value ṁ is measured, the pressure difference ΔP can be adjusted. In this case, the measured mass flow value ṁ serves to monitor whether the permissible operating range B is exceeded.

In 2 a pressure difference ΔP from the first pressure P ₁ and the second pressure P _{2 is} plotted against the mass flow value ṁ. The permissible operating range B can, for example, before the actual operation of the fuel cell stack 2 be determined. This can be possible cathode currents 10 with mass flow values ṁ, for different operating conditions, eg. B. different load conditions of the fuel cell stack 2 , are characteristic, are given and the resulting due to the pressure loss and the current pressure difference .DELTA.P are measured. Depending on temperature, humidity and current intensity at a set mass flow value ṁ, different pressure differences .DELTA.P resulting within an upper tolerance limit B 'and a lower tolerance limit B "may nevertheless result for trouble-free, reliable operation of the fuel cell system 1 are characteristic. The permissible operating range B ensures such. B. in the case of the cathode current 10 as mass flow 10 getting enough oxygen for the electrochemical reaction in the fuel cell stack 2 is available. An insufficient oxygen supply can, for. B. damage to membranes in the fuel cell stack 2 to lead. Alternatively, the different pressure differences ΔP can be adjusted and the permissible mass flow values ṁ can be measured.

The permissible operating range can also be determined or adjusted only during fuel cell operation on the basis of the throttle model according to equation (1). Here, it is initially assumed that the operation is trouble-free, so that the parameters a ₀ , a ₁ and a ₂ can be determined or adjusted, resulting in the permissible operating range B.

Will now the fuel cell system 1 operated at an operating point A within the allowable operating range B and occurs before or in the fuel cell stack 2 on, so sinks by the lower cathode current 10 after the leakage, the pressure difference ΔP, so that the operating point A ¹ below the lower tolerance limit B '' sets. If the mass flow value ṁ is adjusted, the operating point A ¹ remains with existing leakage. If the pressure difference .DELTA.P regulated, the operating point A ¹ will move quickly to the operating point A ² , in which the same pressure difference due to the leakage, a higher mass flow value ṁ is needed. Both the operating point A ¹ and the operating point A ² are located below the permissible operating range B in the in 2 made application. The monitoring unit 14 recognizes that the current operating point A ¹ or A ^{2 is} below the lower tolerance limit B '' and concludes that in the channel 5 before the second pressure sensor 9 a leak must have occurred. In response to this conclusion gives the monitoring unit 14 a warning out and cause the fuel cell system 1 to go into emergency operation. The compressor 3 is set in emergency mode now so that a predetermined pressure difference .DELTA.P can be maintained, which is possible in comparison to normal operation only by an increased mass flow value ṁ. Although this is the maximum power of the fuel cell system 1 limited and the efficiency deteriorates, however, the emergency operation allows the user to the fuel cell system 1 continue to operate without the fuel cell 2 to harm. In case of using the fuel cell system 1 As a motor vehicle drive the emergency operation allows the user to drive to the nearest workshop.

In 3 is again a plot of the pressure difference .DELTA.P over the mass flow value ṁ shown. Also, the allowable operating range B is again shown with the tolerance limits B ', B''. A possible operating point A is within the permissible operating range B. Above at higher pressures is an operating range C, in which at a regulated pressure difference ΔP too low a mass flow value ṁ results, so that there is a shortage of the fuel cell 2 would come with oxygen.

The operating range C can be achieved by the fact that z. B. caused by the electrochemical reaction moisture in the channel 5 condenses and forms droplets. The inventive method recognizes leaving the permissible operating range B, since droplets formation of the operating point A at adjusted pressure difference .DELTA.P to the operating point A ³ with a reduced mass flow value ṁ or with unchanged mass flow value ṁ shifts to the operating point A ⁴ with an increased pressure difference .DELTA.P. Both operating points A ³ , A ⁴ are above the upper tolerance limit B 'in the inadmissible operating range C.

The operating range C can be achieved on the other hand that z. B. in the channel 5 moisture generated by the electrochemical reaction freezes at low outside temperatures, thus reducing the average of the channel, so that the cathode current 10 a higher pressure loss than usual suffers. Thus, even with ice formation, the operating point A at regulated pressure difference on the operating point A ³ and with unchanged mass flow value ṁ on the operating point A ⁴ move. At worst, the channel can 5 completely freeze and the cathode current the fuel cell 2 not reach anymore. Ice formation in the canal 5 can cause the fuel cell system 1 is no longer operational and must be shut down. By means of the present timely detection of ice formation, suitable countermeasures, such as, for example, drying and / or heating, can be taken at an early stage, which control the operation of the fuel cell system 1 to back up.

Detects the monitoring unit 14 in that the upper tolerance limit B 'has been exceeded, the monitoring unit concludes 14 in that either droplet or ice formation is present. If, in addition, the outside temperature is determined, then the monitoring unit 14 also distinguish between droplet and ice formation. In either case, it may reduce the power production of the fuel cell in response to exceeding the upper tolerance limit B ' 2 cause. This results in less water from the electrochemical reaction, which can condense or freeze. Alternatively, the monitoring unit 14 a heating of the channel 5 cause. The channel 5 can be heated for example by hot plates in the fuel cell stack or by warmer cooling water. Heating causes the ice to melt and also results in a higher evaporation rate of the droplets. The channel 5 can also be dried by increasing the mass flow value ṁ.

To freeze water in the canal 5 during a non-operation of the fuel cell 2 To prevent and thus avoid freezing of the water in the membrane and damage to the membrane, when terminating the operation of the channel 5 be blown dry. For this purpose, in particular with a small or missing power production, a possibly increased cathode current 10 through the channel 5 cleverly. In this case, the method according to the invention does not serve to detect a malfunction, but to check whether a desired drying state of the channel has been reached, but in which the membranes of the fuel cell stack are still moist. A range D in the pressure difference ΔP over mass flow value ṁ plot, which corresponds to this desired drying condition and which is below the lower tolerance limit B "(see FIG. 3 ), before the start of operation of the fuel cell system 1 be determined. During drying, the operating point A of the permissible operating range shifts to point A ⁵ at a constant mass flow value ṁ. If a pressure difference ΔP associated with the point A ^{5 is} measured, then the monitoring unit 14 close to the permissible operating range B and the fuel cell system 1 switch off.

If the mass flow value ṁ is not measured, then the monitoring unit can 14 or in another control unit a in 4 illustrated loop structure 18 can be used, which does not require a measurement of the mass flow value ṁ. From a predetermined mass flow value ṁ _target and a first target pressure P _{1, target} is a in a control unit part 19 based on the permissible operating range B, a second setpoint pressure P _{2, setpoint} . In a regulator 20 continue to be measured as input to the measured, through the transmission links 15 . 16 transmit first and second pressures P ₁ and P ₂ . The regulator 20 changes the first and the second setpoint pressure P _{1, set point} and P _{2, should be} such that the measured values P ₁ and P ₂ with the original setpoint pressures P _1, P ₂ and _{Soll 2, should} match and outputs control signals u _R1 , u _R2 , to change the target pressures P _{1, Soll} 'and P _{2, should} ' lead to a flat feedforward control 21 Next, the speed n of the compressor 3 and the control voltage U for the back pressure valve 6 for the cathode current 10 of the fuel cell system 1 pretends. If a control signal u _R1 , u _{R2 exceeds} a tolerance limit, a deviation from the permissible operating range B is assumed and the conclusions drawn in the above examples are drawn. For example, initially the operation of the fuel cell system 1 trouble-free and stationary, so that the set pressures P _1, P ₂ and _{Soll , should} coincide with the measured pressures P ₁ and P ₂ and the controller 20 the set pressures P _{1, setpoint} and P _{2, should} not be changed. Now occurs a leak in the fuel cell 2 on, the second pressure P _{2 is} too high. So that the second pressure P ₂ the target pressure P _{2, should} correspond again, the controller gives 20 a lowered desired pressure P _{2, should} 'off, whereby the control voltage U for the back pressure valve 6 is adjusted so that an increased mass flow value ṁ flows through the fuel system (operating point A ² in 2 ). If there is ice or droplet formation, the second pressure P _{2 is} too low. So that the second pressure P ₂ the target pressure P _{2, should} correspond again, gives the controller 20 an increased setpoint pressure P _{2, should} 'off, whereby the control voltage U for the back pressure valve 6 is adjusted so that a reduced mass flow value ṁ flows through the fuel system (operating point A ³ in 3 ). The increased mass flow value ṁ can thus be recognized at the lowered desired pressure value P _{2, soll} 'and the reduced mass flow value ṁ at the increased desired pressure value P _{2, soll} '. A disturbance may result from a deliberate change of the predetermined target pressure values P _{1, Soll} and P _2, due to a changed power demand on the fuel cell 2 be distinguished by the fact that only the changed target pressure values P _{1, Soll} 'and P _{2, soll} ' are changed.

Would the mass flow value ṁ, however, behind the second pressure sensor Measured in the flow direction, so are the same the figures for ice and droplet formation. however the operating point A is also above the permissible Operating range B in case of leakage, so between the different disorders are no longer distinguished can.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102006008254 A1 [0003]

Claims (15)

Method for operating a fuel cell system ( 1 ) with at least one fuel cell ( 2 ), whereby a mass flow ( 10 ) the fuel cell ( 2 ), characterized in that I. the method comprises a first step for detecting a deviation from a permissible operating range (B), wherein the first step comprises the following individual steps: A. defining the permissible operating range (B) in that a mass flow value ( ṁ) permissible pressure differences (ΔP) from a first pressure (P ₁ ) of the mass flow ( 10 ) in front of the fuel cell ( 2 ) and a second pressure (P ₂ ) of the mass flow ( 10 ) after the fuel cell ( 2 ) within tolerance limits (B ', B'') B. Measuring the first pressure (P ₁ ) before entry of the mass flow ( 10 ) into the fuel cell ( 2 ) at a time C. Measuring the second pressure (P ₂ ) after an exit of the mass flow ( 10 ) from the fuel cell ( 2 ) at the time D. Closing to a deviation from the permissible operating range (B), if an operating point (A, A ¹ , A ² , A ³ , A ⁴ , A ⁵ ) by an assignment of the mass flow value (ṁ) of , in particular at the same time, throughflowing mass flow ( 10 ) to a measured pressure difference (ΔP) from the measured first pressure (P ₁ ) and the measured second pressure (P ₂ ) is characterized, outside the tolerance limits (B ', B'') of the permissible operating range (B) is II that the method includes a second step in which a conclusion is drawn from the deviation from the permissible operating range (B) and the fuel cell system ( 1 ) is caused to a corresponding reaction. A method according to claim 1, characterized in that the permissible operating range (B) in a single step IA, in particular by series of measurements, before the actual operation of the fuel cell system ( 1 ). Method according to claim 1, characterized in that that the permissible operating range (B) in single step I. A. the operating conditions, such as temperature, humidity or generated power of the fuel cell, during operation is adjusted by a throttle model. Method according to one of the preceding claims, characterized in that the mass flow value (ṁ) from single step ID in addition to the individual steps IB and IC, in particular at the same time as the first and the second pressure (P ₁ , P ₂ ), is measured. Method according to Claim 1 or 2, characterized in that the mass flow value (ṁ) from individual step ID is characterized and set by controller signals (u _R1 , u _R2 ), a controller ( 20 ) sets the mass flow value (ṁ) such that the measured first pressure (P ₁ ) and the measured second pressure (P ₂ ) coincide with a first setpoint pressure (P _{1, setpoint} ) and a second setpoint pressure (P _{2, setpoint} ), wherein the second setpoint pressure (P _{2, setpoint} ) is determined by a permissible pressure difference (ΔP) of a predetermined mass flow value (ṁ _soll ) and the predetermined first setpoint pressure (P _{1, setpoint} ), wherein in particular the predetermined mass flow value (ṁ _soll ) is determined by a power demand the fuel cell ( 2 ) is given. Method according to one of the preceding claims, characterized in that the mass flow value (ṁ) a mass flow value (ṁ) before entering the fuel cell ( 2 ), in particular a mass flow value (ṁ) before entry into a compressor ( 3 ) is. Method according to one of the preceding claims, characterized in that when departing from the permissible operating range (B) in step II. To a fault, in particular a leakage and / or a presence of at least one substance in a solid and / or liquid phase within a Channels ( 5 ), the mass flow ( 10 ) flows through, is closed. Method according to one of the preceding claims, characterized in that, if in a plot of the pressure difference (ΔP) above the mass flow value (ṁ) the operating point (A, A ¹ , A ² , A ³ , A ⁴ , A ⁵ ) outside the tolerance limits (B ', B'') and is below the permissible operating range (B), in step II. To a leakage of the channel ( 5 ) in front of or in the fuel cell ( 2 ) is closed. A method according to claim 8, characterized in that in case of leakage in step II. A warning message is generated and the fuel cell system ( 1 ) is converted into an emergency operation. Method according to one of claims 1 to 7, characterized in that when in a plot of the pressure difference (ΔP) above the mass flow value (ṁ) the operating point (A, A ¹ , A ² , A ³ , A ⁴ , A ⁵ ) outside the tolerance limits (B ', B'') and above the permissible operating range (B), in step II. to the presence of at least one substance in a solid and / or liquid phase within the channel ( 5 ) between a first pressure sensor ( 8th ), with which the first pressure (P ₁ ) is measured and a second pressure sensor ( 9 ), with which the second pressure (P ₂ ) is measured, is closed. A method according to claim 10, characterized ge indicates that in step II. in the case of a solid and / or liquid phase within the channel ( 5 ) the channel ( 5 ) or heated by the fuel cell ( 2 ) is reduced or that in the case of a liquid phase within the channel ( 5 ) the mass flow ( 10 ) is increased. Method according to one of claims 1, 2, 4 or 6, characterized in that during a termination of an operation of the fuel cell ( 2 ) the permissible operating range (B) is deliberately left, and the operating point (A, A ¹ , A ² , A ³ , A ⁴ , A ⁵ ) in a range (D) is set, which is outside the allowable operating range (B) but for a dry channel ( 5 ) is characteristic so as to freeze a substance within the channel ( 5 ) and / or the fuel cell ( 2 ) to prevent. Fuel cell system ( 1 ) with at least one fuel cell ( 2 ), whereby a mass flow ( 10 ) through the fuel cell ( 2 ) is conductive, characterized in that in the fuel cell system ( 1 ) a first pressure sensor ( 8th ) for measuring a first pressure (P ₁ ) of the mass flow ( 10 ) in the flow direction in front of the fuel cell ( 2 ) and a second pressure sensor ( 9 ) for measuring a second pressure (P ₂ ) of the mass flow ( 10 ) in the flow direction after the fuel cell ( 2 ) and that the fuel cell system ( 1 ) a monitoring unit ( 14 ), which on the basis of the first pressure (P ₁ ), the second pressure (P ₂ ) and a mass flow value (ṁ) to an operating point (A, A ¹ , A ² , A ³ , A ⁴ , A ⁵ ) outside an allowable Operating range (B) of the fuel cell system ( 1 ) closes. Fuel cell system ( 1 ) according to claim 13, characterized in that the mass flow value (ṁ) is a measured mass flow value (ṁ) and that the fuel cell system ( 1 ) in the flow direction a mass flow sensor ( 7 ), a compressor ( 3 ), the first pressure sensor ( 8th ), the fuel cell ( 2 ), the second pressure sensor ( 9 ) and a back pressure regulating valve ( 6 ) having. Fuel cell system ( 1 ) according to claim 13 or 14, characterized in that it is operable according to a method according to one of claims 1 to 12.